A battery powered cellular telephone includes a number of different types of circuitry. The circuitry can be distinguished generally as RF circuitry and base band circuitry. It is typically the case that the supply voltage requirements of these two types of circuitries differ, with the RF circuitry requiring a higher supply voltage. For example, the RF circuitry power amplifier will generally be operated more efficiently at a higher voltage (e.g., around 4.5 volts) than at a lower voltage at which the base band circuits, such as a central processor unit (CPU) and/or a digital signal processor ((DSP), are typically operated.
It is known in the art to use a number of voltage regulators that provide various supply voltages. However, if a linear voltage regulator is used to provide the lower voltage requirements of the base band circuitry, considerable additional power consumption can occur, as well as an undesirable heating effect. By example, if the regulator is required to provide 3 volts at 10 mA, and is connected across a six volt battery, at total of 0.01 A.times.3 V=0.03 W is generated and must be dissipated.
Alternatively, a lower voltage that supplies the base band circuitry can be stepped up to a higher voltage, such as with a chopper or switched capacitor arrangement, to supply the higher RF circuit voltage. However, this technique is undesirable at least for the reasons that it inherently generates switching noise which can affect circuit operation, and it furthermore may cause an undesirable audible signal.
One could provide two or more cells in series and connect the RF circuitry across all of the cells, while connecting the base band circuitry across fewer cells, thereby providing a lower voltage to the base band circuitry. However, it can be appreciated that this technique will more rapidly discharge the cell or cells that are required to supply both the RF circuitry and the baseband circuitry. An additional problem is created when the cells are recharged, as the cells are recharged in a series configuration. This type of connection between the cells and the loads is obviously an undesirable compromise.